Checking the time intervals

Earlier, we mentioned needing to have equally sized time intervals. Additionally, before we perform any time series analysis, we need to check for the number of non-missing time intervals. So, let's check the number of enrollment years for each category.

Using the dplyr package, we can use summarize (n()) to count the number of entries for each category:

# -- summarize and sort by the number of years 
yr.count <- x2 %>% group_by(cat) %>% summarise(n = n()) %>% arrange(n)

# - we can see that there are 14 years for all of the groups.  That is good!
print(yr.count, 10) 
 > Source: local data frame [24 x 2]
 > 
 >                      cat     n
 >                   (fctr) (int)
 > 1         18 to 24 YEARS    14
 > 2         25 to 34 YEARS    14
 > 3         35 to 44 YEARS    14
 > 4         45 to 54 YEARS    14
 > 5         55 to 64 YEARS    14
 > 6      65 YEARS AND OVER    14
 > 7               ALL AGES    14
 > 8 ...